1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor chips, particularly to a method for processing a semiconductor wafer to be extremely thin and dicing the semiconductor wafer into chips.
2. Description of Related Art
FIG. 3 is a flow chart showing a conventional chip manufacturing process. A plurality of semiconductor devices such as ICs are formed together on the obverse of a wafer and are individually inspected, and the wafer is then diced with a dicing saw to separate the devices. The semiconductor devices for IC cards are required to be thin, and in that case the reverse of the wafer is ground by a back grinder so as to make the wafer in a desired thickness before dicing it into the separate devices.
Before the reverse of the wafer is ground, a protecting sheet is adhered on the obverse of the wafer to protect the semiconductor devices, which have been formed on the obverse, from damages and contamination. After the reverse of the wafer is processed, the protecting sheet is peeled from the obverse of the wafer. Then, a dicing sheet is adhered on the reverse of the wafer, and the wafer is mounted on a frame for dicing so as to be diced.
The wafer whose reverse has been processed is thin and is extremely apt to be broken; thus, the wafer is often damaged when treating the wafer or adhering the dicing sheet on the wafer.
In order to overcome the above-mentioned problem, Japanese patent application laid-open Nos. 5-29455 and 5-63077 disclose methods wherein the dicing sheet is adhered on the reverse of the wafer after the reverse of the wafer is ground before the protecting sheet is peeled from the obverse, and then the protecting sheet is peeled from the obverse and the wafer is diced, so that the thin wafer alone is not treated.
Still, as even thinner wafers have required such as of 30 xcexcm to 50 xcexcm, although the dicing sheet is adhered on the reverse of the wafer, the wafer is damaged as shown in FIG. 4 when the protecting sheet is removed. FIG. 4 is a view of the conventional chip manufacturing process, which shows a state where the protecting sheet is separated from the obverse of the wafer after the reverse of the wafer is processed, and also shows that the wafer is partially broken. This occurs because of the fact that the stress is unevenly distributed in the wafer when removing the protecting sheet, and the stress concentrates at the frailest portion of the wafer.
The present invention has been developed in view of the above-described problems, and has as its object the provision of a process for manufacturing chips of high quality in which, a wafer that can have a large warp and is easy to be broken can be treated when making the final thickness of the wafer extremely thin by a reverse face processing and dicing the wafer into chips, and moreover breakage of the wafer due to concentration of stress is avoided by evenly distributing the stress to the wafer when removing the protecting sheet.
In order to achieve the above-described objects, the present invention is directed to a method for manufacturing a plurality of chips from a wafer, a plurality of semiconductor devices being formed on an obverse of the wafer, comprising the steps of: adhering a protecting sheet with an adhesive on the obverse of the wafer; performing, with respect to a reverse of the wafer, at least one of grinding, polishing, and etching; adhering a dicing sheet on the reverse of the wafer and mounting the wafer on a dicing frame; dicing the wafer with a dicing saw; hardening the adhesive; adhering a separating sheet for separating the protecting sheet over a top face of the protecting sheet; and separating the protecting sheet from the obverse of the wafer by separating the separating sheet from the wafer.
Preferably, the adhesive is an ultraviolet-setting type adhesive; and the obverse of the wafer is irradiated with ultraviolet light in the hardening step. Alternatively, the adhesive is a heat-sensitive type adhesive; and temperature of the wafer is controlled to harden the adhesive in the hardening step.
Moreover, in order to achieve the above-described objects, the present invention is directed to a method for manufacturing a plurality of chips from a wafer, a plurality of semiconductor devices being formed on an obverse of the wafer, comprising the steps of: adhering a protecting sheet with a first adhesive on the obverse of the wafer; adhering a reinforcing plate with a second adhesive on a top face of the protecting sheet; performing, with respect to a reverse of the wafer, at least one of grinding, polishing, and etching; adhering a dicing sheet on the reverse of the wafer and mounting the wafer on a dicing frame; dicing the wafer with a dicing saw; hardening the first adhesive; adhering a separating sheet for separating the protecting sheet over a top face of the reinforcing plate; and separating the protecting sheet and the reinforcing plate from the obverse of the wafer by separating the separating sheet from the wafer.
Preferably, the first adhesive is an ultraviolet-setting type adhesive; the second adhesive is not the ultraviolet-setting type adhesive; the reinforcing plate is made of an ultraviolet light transmissible material; and the obverse of the wafer is irradiated with ultraviolet light in the hardening step. Alternatively, the first adhesive is a heat-sensitive type adhesive; the second adhesive is not the heat-sensitive type adhesive; and temperature of the wafer is controlled to harden the first adhesive in the hardening step.
According to the present invention, the wafer is treated in the state that the protecting sheet is adhered on the obverse of the wafer, or the protecting sheet and the reinforcement sheet are adhered on the obverse of the wafer, or the dicing sheet is adhered on the reverse of the wafer and the wafer is mounted on the frame for dicing; hence a large warp, if any, of the extremely thin wafer can be corrected, and the wafer is treated with reinforcement.
The wafer is diced while the protecting sheet is adhered on the obverse of the wafer.
Further, since the protecting sheet and the reinforcing plate are separated after the wafer is diced into separate chips by dicing, the distribution of the stress to the wafer at the separation is uniform, and thus a partial concentration of the stress to the wafer does not occur.
Furthermore, the adhesive of the protecting sheet is hardened by the irradiation of the ultraviolet light or by the temperature control before separating the protecting sheet from the wafer so as to weaken the adhesive, whereby the wafer at the time of separating the protecting sheet can be even more effectively protected.